title: An apodized SOI waveguide-to-fiber surface grating coupler for single lithography silicon photonics.
abstract: We present the design, fabrication, and characterization of a grating for coupling between a single mode silica fiber and the TE mode in a silicon photonic waveguide on a silicon on insulator (SOI) substrate. The grating is etched completely through the silicon device layer, thus permitting the fabrication of through-etched surface coupled silicon nanophotonic circuits in a single lithography step. Furthermore, the grating is apodized to match the diffracted wave to the mode profile of the fiber. We experimentally demonstrate a coupling efficiency of 35% with a 1 dB bandwidth of 47 nm at 1536 nm on a standard SOI substrate. Furthermore, we show by simulation that with an optimized buried oxide thickness, a coupling efficiency of 72% and a 1 dB bandwidth of 38 nm at 1550 nm is achievable. This is, to our knowledge, the highest simulated coupling efficiency for single-etch TE-mode grating couplers. In particular, simulations show that apodizing a conventional periodic through-etched grating decreases the back-reflection into the waveguide from 21% to 0.1%.
authors.affiliation: Microsystem Technology Laboratory, School of Electrical Engineering, KTH-Royal Institute of Technology, SE-100 44 Stockholm, Sweden. mikael.antelius@ee.kth.se
authors.forename: Mikael
authors.initials: M
authors.lastname: Antelius
authors.forename: Kristinn B
authors.initials: KB
authors.lastname: Gylfason
authors.forename: Hans
authors.initials: H
authors.lastname: Sohlström